Protective assemblies are provided which surround a fuel container, bladder or tank with a material. The material typically employed includes a rigid-cell ballistic foam material positioned surrounding the fuel container or bladder. Fuel containers or bladders on select helicopters are constructed of a reinforced vulcanized rubber material with the rigid-cell ballistic foam material positioned in surrounding relationship to the fuel container or bladder. The rigid-cell ballistic foam material reduces the occurrence of fire with filling voids or pockets within the airframe structure of the aircraft and preventing build-up of fuel vapor. The foam acts to extinguish any sparks resulting from ballistic impacts with airframe components. The foam also provides additional strength to the aircraft structure and slows down the speed of shrapnel during a ballistic event.
Even though certain rigid-cell foam materials employed to surround the fuel container or bladder are capable of attenuating energy by crushing in a crash event, the material is however subject to some amount of rebound since the material can store some energy elastically. The foams used are typically closed cell polyurethane or polyethylene with densities in the range between 1.8 to 5.0 pounds per cubic foot. Surrounding an entire fuel container or bladder with such rigid-cell ballistic foam can add significant weight to an aircraft.
There is a need to provide improved protective assemblies which include fuel containers which attenuate forces or hydrodynamic pressures generated as a result of kinetic energy of the fuel contained within the fuel container or bladder of an aircraft at the time of a crash event. This is particularly the case for those fuel containers or bladders constructed of reinforced vulcanized rubber material or otherwise having a flexible wall construction. There is a need to protect support structures adjoining the fuel container or bladder within the aircraft from the hydrodynamic pressures at the time of a crash event to reduce the occurrence of imparting damage to the support structures. Damage imparted to support structures of the aircraft impedes the ability of the aircraft structure to in turn protect the occupants.
There is also a need to reduce the occurrence of fire upon an occurrence of a rupture of the fuel container or bladder by way of a crash event or as a result of a ballistic event. Also, there is a need to provide protection to support structures within the aircraft, as mentioned above, enabling designers to design lighter weight structures which is beneficial to aircraft manufactures and to the optimization of the operation of the aircraft.